Missing portion of a tubular bone

ABSTRACT

The device relates to reconstructive surgery and orthopedics, and includes a central rod introducible into medullary canals of bone fragments of a bone, and a tubular element fittable on the rod at the place of the missing portion of the bone, the tubular element being equidimensional with the missing portion of the bone. The tubular element is shaped as a shell made of biocompatible polymers, and a layer of a porous polymer material is insertable between the rod and the shell incorporating a biomass of homogenized bone tissues. The invention is used for restoration of missing portions of bone which have been lost due to extensive injuries or wounds or as a result of pathologic changes of the bone tissue (such as may be caused by tumors or tuberculous infections).

FIELD OF THE INVENTION

The invention relates generally to reconstructive surgery andorthopedics and more specifically to a device for restoration of amissing portion of tubular bone.

BACKGROUND OF THE INVENTION

Problems of bone tissue restoration include avoiding free space betweenbone fragments, avoiding filling the space previously occupied by lostbone with connective tissue, and controlled evacuation of the space toleave room for the newly growing tissue.

Solution of the problem lies in the development of biocompatiblepolymers biodegradable under the action of body fluids within presetperiods of time and technological processes for making diversely shapedfinished products from such polymers, as well as technology forimparting therapeutic properties to such polymer products.

Known structures made of biologically inert materials are aimed atpermanent replacement of a missing portion of bone and thus render itcompletely impossible to form fresh bone tissue of the patient's ownmaking at the place involved.

A prior-art device for external immobilization of bone fragments (cf. I.A. Moshkovich, Operative Orthopedics, 1983, Meditsina Publishers,Moscow, pp. 224-225 (in Russian)) has a number of rings inter connectedthrough rods and provided with intramedullary pins. Application of thisdevice enables one to elongate a human limb by daily repeated gradualextension of the bone fragments by gradually increasing the distancebetween the rings. An extension cycle lasts from 20 to 80 days.

Such a device, however, is suitable for stretching sound limbs only.Besides, its application involves much work by medical staff for aprolonged period of time. Also, there is a source of permanent danger ofinfection at the place of introduction of the transverse pins, which mayalso cause contraction of ligaments. The device cannot be used wherethere are extensive total bone defects due to a complicated injury orgunshot wounds.

A state-of-the-art device for restoration of a missing portion of atubular bone (cf. Biomekhanika, 1975, Riga, V. K. Kalnberz, et al.Clinico-biomechanical requirements imposed on the endoprosthesis of thefemoral diaphysis, pp. 365-366 (in Russian)) is known to comprise acentral metallic rod and a tubular element based on biologically inertcomposite materials, such as polymers or inorganic substances, thetubular element being fitted on the rod. The configuration anddimensions of the tubular element correspond to the missing portion ofbone. During surgery, the rod is introduced into the medullary canals ofthe tubular bone fragments, then the tubular element is installed on therod at the place of the missing portion of bone and fixed to the bonefragments. However, such a tubular element is very difficult to makeaccording to the individual dimensions of patient's injury. It isextremely difficult to combine an artificial bone with the bone matrix;the bone tissue is liable to resorb at the place of contact with theartificial bone and the reaction to a large foreign body manifestsitself continuously after implantation of the artificial bone. Thepossibility of replacement by genuine bone of the patient is ruled outcompletely.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a device forrestoration of a missing portion of a tubular bone of a patient's limbwhich would ensure restoration of the function of the limb.

The object is accomplished by providing a device for restoration of amissing portion of tubular bone, comprising a central rod insertableinto the medullary canals of the bone fragments, and a tubular elementmade of a synthetic material and fitted on the rod at the place occupiedby the lost bone portion, the tubular element being equidimensional withthe lost bone portion. The tubular element is shaped as a shell ofpolymer biocompatible with the bone tissue, and a layer of a polymericporous material introducible between the rod and the shell andincorporating a biomass of homogenized bone tissue.

The proposed device provides for regeneration of the bone tissue oflarge areas of the missing bone. This is achieved by appropriateconstruction of the tubular element. Provision of the shell prevents theregeneration zone from being filled with soft tissue and makes itpossible to retain the porous material with the biomass within thevolume of the missing portion of bone in the regeneration process, aswell as determining the geometric dimensions of the bone portion beingrestored. The porous mass plays the part of a matrix, on which theliving bone tissue is formed. Provision of a layer of the porous massbetween the rod and the shell allows efficient fixing of the tubularelement on the rod.

Provision of a biomass of homogenized bone tissues in the porous masspromotes the regeneration process, which leads to a complete restorationof the missing portion of bone.

In a preferred embodiment of the present invention the shell is shapedas a telescopic structure made up of at least two tubular elements. Thismakes it possible to readily change the shell length during surgery instrict accordance with the length of the missing portion of bone, whichmakes possible the regeneration process and cuts down the operatingtime.

According to one of the embodiments of the present invention, the layerof porous polymer material is shaped as a bundle of fibers ofbiocompatible polymers.

Such an embodiment of the invention avoids the presence of free spacebetween the rod and the shell, which adds to the reliability of holdingthe tubular element to the rod and improves the bone tissuesregeneration conditions.

According to another embodiment of the invention the layer of porouspolymer material is made of expanded hydrogel.

Such an embodiment likewise makes it possible to fill the entire spacebetween the shell and the rod, facilitating biomass introduction andcontributing to its uniform distribution and retention in the area ofthe missing portion of bone.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages of the present invention will becomeevident from the following detailed description of some specificexemplary embodiments thereof, with reference to the accompanyingdrawings, wherein:

FIG. 1 is a schematic cross-sectional view of a device, according to theinvention, installed in a tubular bone of a limb; and

FIG. 2 is a schematic cross-sectional view of an embodiment of the shellconstruction.

FIG. 3 is another schematic cross-sectional view of an embodiment of theshell construction.

FIG. 4 is a further schematic cross-sectional view of an embodiment ofthe shell construction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A device of the present invention includes a central rod 1 (FIG. 1)adapted to be introduced into a medullary canal 2 of an injured bone 3,and a tubular element 4 to be fitted on the rod 1 at the place of amissing portion of bone 3 so as to contact both of the bone fragments 5,6 of the bone 3. The dimensions of the tubular element 4 correspond tothe missing portion of bone 3 and tubular element 4 is shaped as a shell7 of polymers biocompatible with the bone tissue. A layer 8 of a porouspolymer material may be introduced between the rod 1 and the shell 7 forincorporating a biomass of homogenized bone tissues.

The shell 7 is shaped as a telescopic structure made up of at least twotubular elements 9, 10 (FIGS. 2 through 4), which are held together. Thelength of the shell 7 should be equal to the length of the missingportion of bone 3. The tubular elements 9, 10 of the shell 7 may beinterlinked with the aid of a bonded joint 11 (FIG. 2), or a stud 12(FIG. 3), as well as by a joint consisting of a recess 13 and a ridge 14(FIG. 4).

The shell 7 is provided with radial holes 15, and fixing-and-supportingelements 16 (FIGS. 1 through 4) are provided on the inner surface of thetubular elements 9, 10.

The layer 8 of porous polymer material may be shaped as a bundle offibers from biocompatible polymers or may be made of expanded hydrogel.

The device is fitted onto a patient as follows.

Prior to installing the device a set of components of the device havinga standard size depending on the diameter of the central rod 1, which inturn correspond to the diameter of the medullary canal 2 of the injuredbone 3, are selected. Upon withdrawing the rod 1, its length is adjustedby cutting so that after having been introduced into the proximalportions of the bone fragments 5, 6 the rod 1 is sized to ensure thesame limb length as before the injury. The coaxial shell 7 is fittedonto the rod 1 approximately in its midportion with the aid of thesupporting element 16, and the porous mass 8 is introduced between therod 1 and the coaxial shell 7 as a bundle of fibers. When the porousmass is expanded hydrogel, it is introduced at a later stage along withthe biomass. Then the rod 1 is introduced into the medullary canals 2 ofboth bone fragments 5 and 6 and the position assumed by the shell 7 iscorrected so that the shell falls within the area of the missing portionof bone 3. Next, the length of the original limb is restored bycompleting the intramedullary introduction of the central rod 1 into thefragments 5, 6 of the bone 3 and the telescopic shell 7 is extendeduntil the length is equal to the length of the missing portion of bone3. As a result, the edges of shell 7 contact the ends of the fragments5, 6 of the bone 3 and the length is fixed with the aid of one of thejoints described above (FIGS. 2 through 4). Thereupon the mass isdispersed and introduced through one of the holes 15 into the porousmass appearing as a bundle of fibers.

When expanded hydrogel 8 is used as the porous mass, the biomass isfirst introduced into the hydrogel and then both the biomass and thehydrogel are introduced jointly through one of the holes 15 in thecoaxial shell 7, into the space between the shell 7, the central rod 1and the bone fragments 5, 6. The mixture is introduced until the biomassor its mixture with the expanded hydrogel 8 appears at the edges of bothfragments 5, 6 of the bone 3. Then the wound is stitched up in layersand additional external immobilization is provided, when necessary.

Medicoexperimental studies of the device were carried out onexperimental dogs. An annular bone fragment 30 to 35 mm long was removedfrom the femoral bone 3 under general anesthesia. A central rod 1 havinga diameter of 8 mm, was introduced into the medullary canals 2 of bothbone fragments 5 and 6 and the telescopic shell 7 was held to the rod 1.The inside diameter of the shell 7 was in excess of the diameter of therod 1 by 5 or 6 mm.

The rod 1 was made of a copolymer of N-vinylpyrrolidone withmethylmethacrylate reinforced with a mixture of capron fibers andaromatic polyamide fibers. A bundle of capron fibers and expandedhydrogel, incorporating an additive of the bone marrow and spongy boneof the same dog, were introduced into the space confined between theshell 7 and the rod 1. Just after surgery a large diastasis was observedbetween the bone fragments 5 and 6, corresponding to the length of theremoved portion of the bone 3. In 141 days after surgery completeregeneration occurred and the medullary canal 2 was clearly discernible.The axis of the bone 3 was correct. The diameter of the restored boneportion was practically equal to the diameter of the original bone 3,only a hardly perceptible thickening of the bone 3 occurring on oneside. Such positive results of experiments on test animals made itpossible to recommend conducting clinical trials. Given below arespecific examples of practical realization of the proposed technicalsolution.

EXAMPLE 1

Male patient V., 42. An area of the comminuted bone 3 38 mm long,resulting from an injury to the shin bone, had a medullary canal 2 of 11mm in diameter. For the bone restoration procedure, use was made of aset, wherein the central rod 1 was a pin of a copolymer ofN-vinylpyrrolidone with methylmethacrylate (the vinylpyrrolidone contentbeing 28 to 32 molar percent) reinforced with capron fiber andincorporating an antimicrobial agent Dioxidine. The pin was shortened tobe equal in length with the medullary canal 2 of the original bone 3 andwas introduced retrogradely into one of the fragments 5 of the bone 3,whereupon the coaxial telescopic shell 7 was held to the pin, the shellbeing made of a copolymer of N-vinylpyrrolidone with butylmethacrylate(the vinylpyrrolidone content being 48 to 56 molar percent), thecopolymer containing 25 percent of a mixture of Dioxidine andQuinoxidine (1:2) and reinforced with four layers of capron fibercontaining Gentamycin. The inside diameter of the shell was 16 mm, whilethe two portions thereof were each 45 mm long. The shells 7 wereprovided with three supporting elements 16 to be held to the rod 1. Oneof the shells 7 (the inner shell) was provided with four pairs ofrecesses 13, whereas the other (outer) shell 7 had four pairs of fixingridges 14. Insertion of the third pair of ridges 14 into the third pairof recesses 13 brought the total length of the shell 7 to about 38 mm.Then a bundle of acid-treated capron fiber was introduced into the shell7. After the rod 1 had been introduced into the bone fragment 6 and theshell 7 had been installed at the place of the bone missing fragment,pulp consisting of residuals of the patient's bone marrow and the spongycomponent of the fragments of the lost bone 3 was introduced into thebundle of fibers through one of the holes 15 until pulp appeared at theedges of the bone fragments 5, 6. Finally, the wound was stitched up inlayers and a coaxial dressing was applied. Complete restoration of thefragment of the missing portion ensued in 86 days.

EXAMPLE 2

Male patient K. Missing portion of the femoral bone, 43 mm long. Acentral rod 1 of 14 mm diameter, made of a pin of a copolymer ofN-vinylpyrrolidone and methylmethacrylate reinforced with modifiedcapron fiber and a coaxial shell 7 having a total length of its twoportions 9, 10 equal to 45 mm, were used. The shell was made of amixture of copolymers (in the ratio of 1:3) of vinylpyrrolidone withmethylmethacrylate and of vinylpyrrolidone with butylmethacrylate,containing 5 percent of Gentamycin and 5 percent of orotic acid,reinforced with capron fiber. The porous mass was introduced between therod 1 and the shell 7, the mass being based on expanded hydrogel from acopolymer of N-vinylpyrrolidone, acrylamide and ethylacrylate, includinga biomass, i.e., homogenate of the bone marrow. After stitching up thewound, an external immobilization apparatus was applied. Completerestoration of the lost fragment of the bone 3 ensued in 94 days.

EXAMPLE 3

Male patient L. Missing portion of the humeral bone, 27 mm long. Use wasmade, as in Example 1, of a rod 1 made of the same material and having adiameter of 9 mm, of the coaxial shell 7 having two portions, 9 and 10,each 25 mm long and made of a mixture of polyethylcyanacrylate and acopolymer of vinylpyrrolidone with butylmethacrylate, containing 20percent of a mixture of Gentamycin, orotic acid, and sea-buckthorn oil(5:4:1) and reinforced with two layers of acid-treated capron fiber. Theporous mass incorporated a mixture of carboxymethyl cellulose fibers andcapron fibers coated with a copolymer of vinylpyrrolidone withbutylmethacrylate, containing Gentamycin, sea-buckthorn oil, andhomogenate of the patient's bone marrow. Complete restoration of thelost portion of bone 3 ensued in 82 days.

EXAMPLE 4

Male patient Sh. Missing portion of the femoral bone 3, 48 mm long. Usewas made, as in Example 1, of a rod 1 made of the same material andhaving a diameter of 12 mm, and of a coaxial shell 7 having two portions15, 16 having four fixing elements each and made of a mixture ofcopolymers of vinylpyrrolidone with methylmethacrylate and ofvinylpyrrolidone with butylmethacrylate, the shell comprising a mixtureof with butylmethacrylate, the shell comprising a mixture of Dioxidineand Quinoxidine and being reinforced with four layers of capron fiber,containing Gentamycin. The porous mass was in the form of a bundle madeup of capron fiber coated with a copolymer and incorporatingsea-buckthorn oil and Gentamycin, and the biomass was in the form of apulp of the spongy bone in donor's blood. After stitching up the wound,a plaster-of-Paris dressing was applied. Complete restoration of thelost portion of bone took 102 days.

To proposed device makes it possible to completely restore missingfragments of tubular bones, involving formation of a patient's own boneof the original dimensions.

A total treatment course with the use of a prior art device rangesbetween 300 and 360 days, whereas that with the use of the proposeddevice lasts from 90 to 100 days. No complications after application ofthe proposed device occurred.

The invention finds utility when applied to restoration of missingportions of bone due to total defects of long tubular bones followingextensive injuries or wounds, or after large pathological changes of thebone tissue (e.g., tumors or tuberculous infections).

What is claimed is:
 1. A device for restoration of a missing portion ofa tubular bone, comprising a central rod (1) insertable into a medullarycanal (2) of distal and proximal fragments (5, 6) of a bone (3) and atubular element (4) disposed coaxially on the rod (1) in place of themissing portion of the bone and being radially substantiallyequidimensional at each end with the missing portion of the bone (3),wherein the tubular element (4) comprises a shell (7) of adjustablelength made from polymers biocompatible with the bone tissue, and alayer (8) of porous polymer material incorporating homogenized bonetissue is disposed between the rod (1) and the shell (7).
 2. A device asclaimed in claim 1, wherein the shell (7) is a telescopic structurecomprising at least two tubular elements (9, 10).
 3. A device as claimedin claim 1, wherein the layer (8) of comprises porous polymer materialbundles comprises bundles of fibers.
 4. A device as claimed in calim 1,wherein the layer (8) of a porous polymer material comprises formedhydrogel.